Automobile drivelines generally provide some level of deceleration when the driver releases the accelerator pedal. In conventional internal combustion vehicles with automatic and manual transmissions, this is a function of the transmission gear and the amount of engine drag, and is always present. In hybrid/electric vehicles, this is provided by regenerative braking torque used to recharge a battery, which provides power to a traction motor to propel the vehicle. In some vehicles, particularly hybrid/electric vehicles and vehicles with dual dry clutch transmissions, the amount of driveline deceleration can be reduced or unavailable depending on various parameters.
The popularity of hybrid electric, plug-in hybrid, and fully electric vehicles continues to increase over time. Accordingly, the prior art is replete with different systems, control technologies, and processes related to the operation of such vehicles. A hybrid electric vehicle (HEV) includes a rechargeable energy storage system (ESS) which is usually configured as a rechargeable battery or battery pack having a relatively high energy density. An HEV can also include a gasoline, diesel, or alternative fuel internal combustion engine. Other vehicle designs may employ a fuel cell and/or another power source in place of or in conjunction with an internal combustion engine in order to further reduce vehicle emissions and improve the operating range of the vehicle. A fully electric vehicle (EV) only includes an electric drive train, e.g., an electric motor and an ESS.
In certain HEV and EV designs, the drive wheels of the vehicle remain continuously connected to the driveline to enable regenerative braking capability, thus providing a relatively efficient means of capturing useful and otherwise wasted braking energy during coastdown and/or during active braking. As is known in the art, an electric motor/generator (MOGEN) can be selectively operated in such a manner as to allow the device to act as a generator during coastdown or an active regenerative braking event. When acting as a generator, the electric MOGEN recharges the ESS while applying a negative torque to the drive wheels and/or the drive shaft, thus electronically slowing the vehicle. The electric MOGEN likewise can be selectively operated as an electric motor, thus drawing stored electrical energy from the ESS as needed to propel the vehicle.
Regeneration during coastdown or active braking contributes to the deceleration of the vehicle. In this regard, negative coastdown regenerative torque can be applied to mimic the engine drag characteristics of a traditional non-electric vehicle. Moreover, negative braking regenerative torque can be applied as a function of brake pedal travel to mimic the characteristics of a standard vacuum-based hydraulic brake system. In practice, braking regenerative torque can be applied as an additive torque to the friction brake torque (which is generated in response to driver actuation of the brake pedal), which allows lower cost and complexity as opposed to fully-blended regenerative braking systems.
In certain situations, the vehicle may have little to no capacity to handle regenerative torque. For example, if the high voltage ESS is fully charged (or has a sufficiently high state of charge), then regenerative torque may be unavailable. As another example, during wheel slip conditions the regenerative braking system may be temporarily disabled to enable an automatic braking system, a traction control system, and/or other systems to immediately initiate and operate. Also cases in which multiple-mode hybrid transmissions shift between modes/gears. In other scenarios, it may not be possible to carry regenerative torque through a shifting operation (or it may be desirable to inhibit regenerative torque during shifting for various reasons, e.g., to reduce noise or vibration). When regenerative torque is unavailable for any reason, then the actual vehicle deceleration will be less than expected due to the loss of deceleration: the coastdown regenerative torque and the additive braking regenerative torque. The perceived difference in deceleration is a function of the normal levels of regenerative torque. For example, if the coastdown deceleration is calibrated to a higher level to allow one pedal driving, then the loss of regenerative torque will be more noticeable than if it were calibrated to a more traditional value in line with engine drag.
Similarly, in some non-hybrid vehicles such as vehicles with dual dry clutch transmissions, the deceleration from the driveline may be unavailable. In the case of dual dry clutch transmissions, the clutch may become overheated and will therefore be forced to open. The deceleration due to engine drag will then not be transmitted to the drive axle. In this case, the application of the friction brakes will restore the feeling of normal coastdown deceleration.
Accordingly, it is desirable to have a vehicle control system that addresses the scenarios mentioned above. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.